Containers made from fibreboard are used widely in many industries. For example, fibreboard containers are used to ship products that are moist or packed in ice such as fresh produce or fresh seafood. It is known that when such containers take up moisture, they lose strength. To minimize or avoid this loss of strength, moisture-resistant shipping containers are required.
Moisture-resistant containers used to date have commonly been prepared by saturating cellulose based substrates with melted wax after folding and assembly. Wax-saturated containers cannot be effectively recycled and must generally be disposed of in a landfill. In addition, wax adds a significant amount of weight to the cellulose based substrate, e.g., the wax can add up to 40% by weight to the cellulose based substrate.
Other methods for imparting moisture resistance to cellulose based substrates have included impregnation with a water-resistant synthetic resin or coating the blank with a thermoplastic material. In the latter case, forming water-resistant seals around cellulose based substrate peripheral edges and edges associated with slots or cutouts in the cellulose based substrate has been an issue. When seals along these edges are not moisture resistant or fail, moisture can be absorbed by the cellulose based substrate with an attendant loss of strength. In addition, obtaining consistent and reproducible bonding of the thermoplastic material to the cellulose based substrate and around edges has been a challenge.
Faced with the foregoing, the present inventors have worked to develop a method for producing a cellulose based substrate encapsulated with a moisture-resistant film that is recyclable and lighter in weight than previous wax-saturated containers and does not suffer from inconsistent bonding, sealing and conformance of a film to the substrate.